Process for making plastic closures and closure

ABSTRACT

A process for realizing plastic capsules ( 1 ) comprises: a first forming stage for realizing a cap ( 2 ) having an internal annular projection ( 2   a ) arranged in proximity of an open lower zone of the cap ( 2 ); a second forming stage of an annular element ( 3 ), provided with a security element ( 4 ) and with an external annular projection ( 3   a ) for inserting, during an assembly stage of the cap ( 2 ) with the annular element ( 3 ), over the internal annular projection of the cap ( 2 ). A stage of mechanical working is performed on the cap ( 2 ), for realizing, on an internal wall of the cap ( 2 ) and in proximity of a lower zone thereof, an annular incision ( 2   b ) which does not pass entirely through the cap ( 2 ) and which receives at least a part of the external annular projection ( 3   a )

TECHNICAL FIELD

The invention relates to a process for realising plastic capsules and the capsule obtained with the process.

BACKGROUND ART

For closure of containers such as bottles for water, soft drinks and liquids in general, widespread use has been made for some time of closure capsules which include, briefly, a cap which serves to open and re-close the container, and a device, generally a security strip, which allows verification of whether the container has already been opened; these capsules, being used to close the necks of the containers having a circular perimeter, normally have a circular shape, at least in the lower part thereof destined to couple with the neck of the container. In particular reference is made to capsules, of a generally known type, which are made in two parts, the first of which parts constitutes the cap with functions of opening and re-closing the container to which the capsule is destined, and the second part thereof consisting in an annular element, among other things provided with a security strip which breaks on first opening of the capsule, destined to constitute a connecting organ between the cap and the container. In some applications the second element exhibits a central zone (for example a disc, although it could be another element) which, during assembly of the capsule detaches from the second element and is positioned in the first element (in the case of the disc, it detaches and is arranged internally of the cap, in the upper part thereof, where it constitutes a seal).

These two elements are realised separately and are thereafter assembled before being inserted on the container; to enable a solid assembly between the two parts which constitute the capsule, the cap is normally provided with an internal annular projection in which, during the assembly stage, an external annular projection exhibited by the second element inserts. Generally these capsules include security strips which are connected to the second element by easy-break zones, with some ribs or zones however that are difficult to break; the security strips also include breakable zones which enable peripheral opening of the security ring on first opening of the container; this is to prevent apart of the capsule, in particular the security ring, from completely detaching from the capsule and remaining attached to the container.

To manufacture these capsules, for some time now injection-moulding and compression-forming technologies have been used: the first includes injection of fluid-state material internally of dies where the material solidifies, while the second includes introducing a piece of plastic material internally of the bottom die of a die and subsequently deforming it by means of a punch which penetrates into the bottom die and forces the material to occupy all the space left between the bottom die and the punch, which space has, obviously, the same conformation as the desired capsule

The injection technology, which uses more complex and expensive dies, enables more complex capsules to be formed. Compression technology has the advantage of using rather simple dies which can be inserted, for example, in rotary machines which comprise a large number of die-punch pairs, which are extremely fast and which render a very high productivity; compression-forming is also a more stable process which is easier to set up, and which also provides greater repeatability in the forming process.

As previously mentioned, both the moulding technologies and the previously-described capsules have been known for a considerable time.

As the present moulding processes, in particular compression-forming, do not enable large undercuts to be produced, it can happen that the anchoring connection between the cap and the second element, which as mentioned is realised by a projection of the second element which inserts in the internal annular projection (which is an undercut) the cap is provided with, is not such as to prevent, on opening the container, a detachment of the second element from the cap; this means that the second element remains on the neck of the container. This fact, in particular in the case of glass containers, is irritating in a case where the container is destined for material recycling, but is extremely damaging in a case where the container, in particular a glass bottle, is destined for re-use. In order to be re-used, these containers are inserted in continuous machines which operate at very high speed and the functioning of which can be seriously compromised by a plastic ring still in place around the container neck.

A main aim of the present invention is to provide a process, and a capsule, thanks to which it is impossible for a part of the capsule to remain anchored to the container closed by the capsule.

An advantage of the process of the invention is that it can also be applied to capsules of known type, with no need to modify the dies used for the realisation thereof.

These aims and advantages and more besides are all attained by the invention as it is characterised in the appended claims.

DISCLOSURE OF INVENTION

Further characteristics and advantages of the present invention will better emerge from the detailed description that follows of a possible actuation of the process, and a possible embodiment of the capsule of the invention, illustrated purely by way of non-limiting example in the accompanying figures of the drawings, in which:

FIG. 1 is a partially-sectioned view in an axial plane of a cap of a known-type capsule;

FIG. 2 is a partially-sectioned view in an axial plane of the cap of the capsule of the invention;

FIG. 3 shows, in an axial section, the annular element applicable both to known-type capsules and to the capsule of the invention;

FIG. 4 is a detail in enlarged scale of the annular element inserted in the cap of a known-type capsule;

FIG. 5 is a detail in enlarged scale of the annular element inserted in the cap of the capsule of the invention.

The process of the invention is for realising capsules 1 made of a plastic material, formed in at least two pieces. The capsule is provided, as are many capsules of known type, with a cap 2, which can be of various shapes, normally cylindrical or slightly truncoconical, and which can also be of various sizes, and which is destined to enable opening and re-closing of a container destined to receive the capsule. The cap is provided with an internal annular projection 2 a which is arranged in proximity of a lower open zone thereof. The capsule further comprises an annular element 3, which is provided with a security element 4, frequently constituted by an annular strip connected to the annular element by means of easy-break zones; the annular element is further provided with an external annular projection 3 a which, during the stage of assembly of the cap and the annular element, inserts above the internal annular projection 2 a of the cap in order to realise an anchoring between the cap and the annular element. Sometimes, as occurs in some known capsules, the annular element is provided, in a central zone thereof, with an additional element which when the capsule is assembled detaches from the second element and positions in the first element; merely by way of example, this additional element (not illustrated as not vital to the aims of this invention) can be a disc which, when the capsule is assembled, detaches from the second element and positions itself in the internal upper part of the cap, there constituting a seal.

The invention provides, in particular, a process and a capsule, of the type described herein above, which render the anchoring between the cap and the annular element more solid with respect to known capsules of this type.

The process comprises a first forming stage for realising the cap 2 and a second forming stage for realising the annular element 3.

The process further comprises, after the first cap-forming stage, a mechanical stage of working on the cap, which is aimed at realising, on the internal wall of the cap and in proximity of a lower zone thereof, an annular incision 2 b which does not pass entirely through the plastic, and which is destined to receive, during the cap assembly stage with the annular element, at least a part of the external annular projection 3 a of the annular element 3. This mechanical working stage is performed before the assembly stage, in which, as occurs with known-type capsules, the cap and annular element are assembled together in order to constitute the finished capsule, ready for use in closing a container.

The mechanical working stage is preferably realised with a cutting stage which is done using blades provided with a shaped cutting surface, which blades insert into the wall of the cap from inside and in the radial direction of the cap.

The mechanical working stage is performed in order that the zone of the cap in which the incision 2 b is realised maintains a resistance to breakage which is superior to that of all the easy-break zones which connect the security element 4 to the annular element 3; therefore, in brief, the incision is not a through-incision and involves only a part of the thickness of the lateral wall of the cap, leaving, at the position of the incision, a residual thickness of the wall which is such as not to constitute an easy-break zone, i.e. not like the connection realised between the annular element and the security strip. This is obviously in order, during a first opening of the container, to prevent the capsule from breaking at the position of the incision and not, as instead is desired, at the position of the easy-break ribs of the security device.

The stage of mechanical working of the cap is done after first heating the cap and preferably after heating the lower part of the cap in which the mechanical operation is to be performed. The heating is preferably done by gripping the lower part of the cap between a pair of jaws heating to a temperature comprised between 40° C. and 60° C. The jaws, which are equipped on the apparatus performing the mechanical operation on the cap, apart from heating the cap also have the function of keeping it still during the mechanical operation.

This stage of heating makes the mechanical working easier to do.

During the mechanical working stage there is also an aspiration stage, performed with normal and known aspirating means, with which in the working zone the portions of cap (plastic shavings or pieces) detached from the cap during the work operation by the tools performing the mechanical operation are aspirated; this is so that, apart from avoiding obvious problems of cleanliness in the environment, is to prevent the shaved pieces of cap from obstructing the functioning of the machines carrying out the various operations.

With the described process caps are obtained which, apart from comprising the above-indicated element, also provide a cap having, in the internal wall thereof and in proximity of the lower zone thereof, an non-through annular incision 2 b which is destined during the assembly stage of the cap with the annular element 3 to receive at least a part of the external annular projection 3 a of the annular element 3. Further, in the caps of the invention the zone of the cap in which the incision 2 b is made exhibits a resistance to breakage which is superior to the resistance of all the easy-break zones which connect the security element 4 to the annular element 3. The incision 2 b is made in such a way that it is arranged superiorly of the internal annular projection 2 a with respect to the open lower zone of the cap.

During the cap assembly stage, the external annular projection 3 a of the annular element 3 bends downwards during its interference with the internal annular projection 2 a of the cap, and once in place is arranged above the projection.

In known capsules the external annular projection 3 a of the annular element 3 is bent down and, following traction upon first opening of the capsule, the external annular projection 3 a can slide downwards until it overcomes the obstacle represented by the projection 2 a and causes the detachment of the annular element 2 from the cap 3; this situation is illustrated in FIG. 4. The element 2 can therefore remain about the neck of the container when closed by the capsule, creating the above-described drawbacks.

Differently to what happens with known capsules, in the capsule of the invention at least a part of the external annular projection 3 a of the annular element 3 inserts internally of the incision 2 b; thus any downwards-directed slippage of the projection 3 a is prevented, and thus any possibility of detachment of the annular element 3 from the cap 2; this situation is illustrated in FIG. 5.

Both the external annular projection 3 a and the incision 2 b which have been described interest the whole perimeter of the elements to which they are applied, i.e. the projection and incision are continuous. This very much facilitates the assembly stage of the capsule which is not constrained to the reciprocal angular position of the parts to be assembled. It would however be possible, should the parts to be assembled have elements imposing a certain angular position of assembly, to realise the projection and incision as discontinuous elements. It is further evident that the incision can be realised by means of tools having different shapes and angles, so that the incision could be shaped or not perpendicular to the cap wall; in particular it might be convenient to realised a downwards-inclined incision.

The described process can be used both for caps made by injection-moulding and for caps made using compression-forming. This process is in any case particularly useful in a case where the first cap-forming stage is a compression-forming stage; the compression-forming process is the process which presents the greater difficulties in realising undercuts, such as the internal annular projection 2 a of the cap 2. With the described process it is possible to maintain the advantages of the compression forming while eliminating the disadvantages, in particular the danger of detachment of the parts making up the capsule, which danger the compression-forming process presents, due to the difficulty of realising very pronounced undercut parts. 

1. A process for realising capsules (1) made of plastic, comprising: a first forming stage for realising a cap (2), which cap (2) is destined to enable opening and re-closing of a container to which the cap (2) will be applied, which cap (2) is provided with an internal annular projection (2 a) arranged in proximity of an open lower zone of the cap (2); a second stage of forming to realise an annular element (3), provided with a security element (4), connected to the annular element (3) by easy-break zones, and further provided with an external annular projection (3 a) for inserting, during an assembly stage of the cap (2) with the annular element (3), over the internal annular projection of the cap (2); wherein after the first forming stage and before the assembly stage of the cap (2) with the annular element (3), a stage of mechanical working is performed on the cap (2), for realising, on an internal wall of the cap (2) and in proximity of a lower zone thereof, an annular incision (2 b) which does not pass entirely through the cap (2) and which, during the assembly stage of the cap (2) with the annular element (3), receives at least a part of the external annular projection (3 a) of the annular element (3).
 2. The process of claim 1, wherein the stage of mechanical working is performed in such a way that a zone of the cap (2) in which the incision (2 b) is made maintains a resistance to breakage which is higher than a resistance to breakage of all of the easy-break zones which connect the security element (4) to the annular element (3).
 3. The process of claim 1, wherein the mechanical working stage comprises a stage of cutting performed by blades having shaped cutting edges.
 4. The process of claim 3, wherein the cutting stage is performed by insertion of one or more blades into the cap (2) wall, entering the cap (2) from the open end thereof and cutting in a direction which is a radial direction of the cap (2).
 5. The process of claim 1, wherein it comprises a stage of aspiration of portions of cap (2) which become detached from the cap (2) during the mechanical working stage.
 6. The process of claim 1, wherein the first forming stage is a stage comprising compression forming.
 7. The process of claim 1, wherein the stage of mechanical working is performed after heating the cap (2).
 8. The process of claim 7, wherein during the stage of mechanical working at least the lower part of the cap (2) is closed between a pair of jaws which are heated to a temperature comprised between 40° C. and 60° C.
 9. A capsule made according to the process of claim 1, comprising: a cap (2) destined to enable opening and re-closing of a container to which the cap (2) is to be assembled, which capsule is provided with an internal annular projection (2 a) arranged in proximity of the lower open zone of the cap (2); an annular element (3), provided with a security element (4) connected to the annular element (3) by easy-break zones, and provided with an external annular projection (3 a) which inserts, during the assembly stage of the cap (2) to the annular element (3), over the internal annular projection (2 a) of the cap (2); wherein the cap (2) comprises, in an internal wall thereof in proximity of a lower zone thereof, an annular incision (2 b) which does not pass entirely through the wall of the cap (2) and which is destined at least partially to receive the external annular projection (3 a) of the annular element (3) during the assembly of the cap (2) with the annular element (3).
 10. The capsule of claim 9, wherein the zone of the cap (2) affording the incision (2 b) exhibits a resistance to breakage which is higher than a resistance to breakage of the easy-break zones which connect the security element (4) to the annular element (3).
 11. The capsule of claim 9, wherein the incision (2 b) is arranged above the internal annular projection (2 a) with respect to the open lower zone of the cap (2). 